From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Matt Sealey <matt@genesi-usa.com>,
Linux ARM Kernel ML <linux-arm-kernel@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
John Stultz <john.stultz@linaro.org>,
Ben Dooks <ben@simtec.co.uk>
Subject: Re: One of these things (CONFIG_HZ) is not like the others..
Date: Mon, 21 Jan 2013 21:03:41 +0000 [thread overview]
Message-ID: <20130121210341.GW23505@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <201301212041.17951.arnd@arndb.de>
On Mon, Jan 21, 2013 at 08:41:17PM +0000, Arnd Bergmann wrote:
> On Monday 21 January 2013, Matt Sealey wrote:
> >
> > ARM seems to be the only "major" platform not using the
> > kernel/Kconfig.hz definitions, instead rolling it's own and setting
> > what could be described as both reasonable and unreasonable defaults
> > for platforms.
No, you've got this totally wrong.
They're not defaults. And I object to your use of "unreasonable" too.
I've no idea where you get that from.
There's a reason why we have different HZ rates - some platforms just
can't do the standard 100Hz tick rate. No way - their timers can't
divide down to that interrupt rate. Sorry to spoil your ivory tower
with a few facts, but your statement is just rediculous.
The reason we don't use kernel/Kconfig.hz is precisely because of that;
we _HAVE_ to have different HZ definitions on different platforms, and
you'll notice that kernel/Kconfig.hz makes _no_ prevision for this.
Now, while things have moved forwards and we have clocksource/clockevent
support, not every platform can support this timekeeping structure;
ebsa110 certainly can't. There's one timer and one timer only which
is usable, which even needs to be manually reloaded by the CPU. No
other independent counter to act as a clock source.
As for Samsung and the rest I can't comment. The original reason OMAP
used this though was because the 32768Hz counter can't produce 100Hz
without a .1% error - too much error under pre-clocksource
implementations for timekeeping. Whether that's changed with the
clocksource/clockevent support needs to be checked.
It's entirely possible with the modern clocksource/clockevent support
that many of these platforms can have their alternative HZ tick rates
removed - but there will continue to be a subset which can't, and all
the time that we have such a subset, kernel/Kconfig.hz can't be used
without modification.
next prev parent reply other threads:[~2013-01-21 21:04 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-21 20:01 One of these things (CONFIG_HZ) is not like the others Matt Sealey
2013-01-21 20:41 ` Arnd Bergmann
2013-01-21 21:00 ` John Stultz
2013-01-21 21:12 ` Russell King - ARM Linux
2013-01-21 22:18 ` John Stultz
2013-01-21 22:44 ` Russell King - ARM Linux
2013-01-22 8:27 ` Arnd Bergmann
2013-01-21 22:20 ` Matt Sealey
2013-01-21 22:42 ` Russell King - ARM Linux
2013-01-21 23:23 ` Matt Sealey
2013-01-21 23:49 ` Russell King - ARM Linux
2013-01-22 0:09 ` Matt Sealey
2013-01-22 0:26 ` Matt Sealey
2013-01-21 21:14 ` Matt Sealey
2013-01-21 22:36 ` John Stultz
2013-01-21 22:49 ` Russell King - ARM Linux
2013-01-21 22:54 ` Matt Sealey
2013-01-21 23:13 ` Russell King - ARM Linux
2013-01-21 23:30 ` Matt Sealey
2013-01-22 0:02 ` Russell King - ARM Linux
2013-01-22 0:38 ` John Stultz
2013-01-22 0:51 ` John Stultz
2013-01-22 1:06 ` Matt Sealey
2013-01-22 1:18 ` Russell King - ARM Linux
2013-01-22 1:56 ` Matt Sealey
2013-01-22 1:31 ` John Stultz
2013-01-22 2:10 ` Matt Sealey
2013-01-31 21:31 ` Thomas Gleixner
2013-01-21 21:02 ` Matt Sealey
2013-01-21 22:30 ` Arnd Bergmann
2013-01-21 22:45 ` Russell King - ARM Linux
2013-01-21 23:01 ` Matt Sealey
2013-01-21 21:03 ` Russell King - ARM Linux [this message]
2013-01-21 23:23 ` Tony Lindgren
2013-01-22 6:23 ` Santosh Shilimkar
2013-01-22 9:31 ` Arnd Bergmann
2013-01-22 10:14 ` Santosh Shilimkar
2013-01-22 14:51 ` Russell King - ARM Linux
2013-01-22 15:05 ` Santosh Shilimkar
2013-01-28 6:08 ` Santosh Shilimkar
2013-01-29 0:01 ` John Stultz
2013-01-29 6:43 ` Santosh Shilimkar
2013-01-29 10:06 ` Russell King - ARM Linux
2013-01-29 18:43 ` John Stultz
2013-01-22 17:31 ` Arnd Bergmann
2013-01-22 18:59 ` John Stultz
2013-01-22 21:52 ` Tony Lindgren
2013-01-23 5:18 ` Santosh Shilimkar
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